This present invention relates to a method of preparing a fabric softening material, in particular to a method of preparing a softening material comprising one or more C.sub.8 -C.sub.28 alkyl or alkenyl groups which are connected to the softener molecule via an ester linkage.
It has been proposed in U.S. Pat. No. 4,767,547 corresponding to EP 239 910 (Procter & Gamble) to incorporate ester linked quaternary ammonium compounds in fabric softening compositions. U.S. Pat. No. 3,915,867 (Stepan) discloses the use of N-methyl,N,N-di(beta-C.sub.14-18 acyloxyethyl) N-beta-hydroxy ethyl ammonium methosulphate in softening compositions. Other ester linked softener materials are described in U.S. Pat. No. 4,137,180 (Lever Brothers). Softener materials comprising ester linkages are especially preferred for use in fabric conditioning compositions for environmental reasons.
A problem with softener materials comprising ester linkages is that they tend to have a relatively high pour point. Pour point can be defined as the lowest temperature at which an active material can be observed to flow or at which temperature the active becomes mobile. (As explained in The Analysis of Fats and Oils by V. C. Mehlenbacher, The Garrard Press, Champaign, Ill. 1960). A high pour point renders the softener materials difficult to process. For example, the softener materials as described in U.S. Pat. No. 4,137,180 (Lever Brothers) have high pour points meaning that they are hardly pumpable at ambient temperature and are difficult to disperse in water.
It is an object of the present invention to solve the above mentioned problem and to provide a process for the preparation of ester linked softener materials.
In the preparation of ester linked softener materials it is known to use a base material, which is similar to the final softener molecule, excepting that it does not comprise the alkyl or alkenyl groups connected to the molecule via an ester linkage. This base material is then reacted with one or more alkyl or alkenyl group containing materials, such that one or more alkyl or alkenyl groups become attached to the base material via an ester-linkage. Finally the material may optionally be subjected to further processing steps, for example quaternization or neutralization, to form the end-product.
For example in U.S. Pat. No. 3,915,867 (Stepan) a process for the preparation of an ester-linked quaternary ammonium material is disclosed, wherein triethanolamine as the base material in the presence of a sodium methoxide solution is reacted with a fatty acid methyl ester mixture in an esterification reaction to form a molecule wherein two alkyl chains are connected to the base molecule via an ester linkage. The molar ratio of fatty acid methyl ester to triethanolamine is 2:1.
In U.S. Pat. No. 4,137,180 (Lever Brothers) a similar method of preparation is disclosed, wherein di-methyl-amino-propane 1,2-diol as the base material is reacted with tallow fatty acids in an esterification reaction to form a molecule, wherein two alkyl groups are connected to the base molecule via ester links.
The described process may use an excess of tallow fatty acids to base material, although this is not preferred. It is further stated that if the molar fatty acid to base is greater than 2:1, free fatty acid remains in the product and is neutralized by alkali at a later step to form soap, which is also not desirable.
U.S. Pat. No. 4,137,180 further requires that the ester-linked quaternary ammonium material must be purified, for example, by recrystallization to remove excess fatty acid from the final product.
An alternative method of preparation is disclosed wherein glycidyl trimethyl ammonium chloride as the base material is reacted with tallow fatty acid anhydride to form a mixture of monoester and diester quaternary ammonium salt in a weight ratio of 3:1 diester to monoester.